As far as I know the switch only keeps the tractor from starting. You must have the clutch depressed for the engine to turn over. You have something else wrong if your clutch will not disengage when pedal is released.
Thanks Eddie; In view of the fact that the tractor will start without the clutch being depressed can I assume the switch is 'malfunctioning'/not working at all?
Maybe. On one of mine the switch worked but someone bypassed it since they were apparently annoyed by having to push in the clutch to start the machine. It's not a bad habit to do regardless if the switch works or not.